Fie x lungimea drumului
in prima zi a parcurs 40x/100=2x/5
in a II a zi a parcurs 3/8(x-2x/5)=3/8·3x/5=9x/40
in a III a zi a parcurs 36 km
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⁸⁾2x/5+¹⁾9x/40+⁴⁰⁾36=⁴⁰⁾x
16x+9x+1440=40x
25x+1440=40x
15x=1440 ⇒x= 1440÷15 ⇒ x=96 km
Deci lungimea drumului a fost de 96 km !